Synergistic effect of fermi level modulation and valence band regulation in mohite Cu2SnS3 for thermoelectric applications

Abstract

The p-type Cu2SnS3 compounds have been experimentally identified as a promising thermoelectric material. Here, we demonstrate the p-type nature of mohite Cu2SnS3 using experimental techniques as well as density functional theory calculations. The experimental results have shown that Ga substitution at the Sn site remarkably enhances the hole concentration and electrical conductivity, reduces the bandgap, and decreases the thermal conductivity, resulting in increased figure of merit. First principle calculations have indicated that Ga substitution changes the electronic structure of Cu2SnS3, primarily due to the reduction in lattice volume and interatomic bond distances. Notably, the appearance of DOS states near the Fermi level has been significantly increased, driven by enhanced hybridization among Cu 3d, Ga 4p, Sn 5p, and S 3p orbitals, which has led to increased electrical conductivity of Cu2Sn0.80Ga0.20S3 to 79 S/cm. Moreover, the substitution of Ga in Cu2SnS3 modifies the electronic structure of Cu2SnS3 substantially, especially the density of states near fermi level is increased, which leads to high carrier concentration of 9.38 × 1020 cm−3, power factor of 329 μW/mK2, and lattice thermal conductivity of 0.50 W/mK, thus high zT of 0.4 is realized in Cu2Sn0.70Ga0.20S3.